1. Field of the Invention
The present invention relates to a fluorescent material coating apparatus that can effectively apply a fluorescent solution to inner surfaces of glass tubes for fluorescent lamps and dry the fluorescent solution applied on the inner surfaces at a uniform drying temperature, and a method of coating the fluorescent substance using such an apparatus.
2. Description of the Related Art
Generally, a fluorescent lamp is classified as a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL). Since the EEFL has high light emission quality, a long service life, and low power consumption, and it can be manufactured in a compact size, it has recently been used as a backlight for a liquid crystal display (LCD).
The EEFL includes a glass tube having an inner surface coated with a fluorescent material. After a predetermined amount of argon gas and mercury is injected into the glass tube, it is sealed. Opposite ends of the glass tube are each enclosed with two electrodes for applying an electric current thereto.
The EEFL is manufactured through a series of processes such as coating the fluorescent material on the inner surface of the glass tube, injecting the light emission gas and mercury into the glass tube, sealing the glass tube, and enclosing the opposite ends of the glass tube with the electrodes.
The fluorescent material coating process is one of the most important processes for determining the light emission quality of the fluorescent lamp. The fluorescent material coated on the inner surface of the fluorescent lamp functions to excite ultraviolet rays to emit visible light when the ultraviolet rays are emitted by collisions between electrons and mercury atoms after the discharge of electrons.
The fluorescent material coating process includes a process of applying a fluorescent solution on an inner surface of the glass tube and a process for drying the applied fluorescent solution. The fluorescent material coating process is performed by a rotary method in which first ends of three to five glass tubes are inserted into holes formed along a circumference of a disk-shaped stage that has a coating section and a drying section, and the fluorescent material is coated as the stage rotates.
The fluorescent solution used in the coating process is a mixture containing an organic solvent, a binder, and a settling agent. The organic solvent may be a volatile organic solvent such as butyl-acetate.
The glass tube that is applied with the fluorescent solution is dried by volatilizing the organic solvent by supplying hot air at a temperature of about 150° into the glass tube.
Particularly, in the drying process, it is important to dry the applied fluorescent solution such that a thickness of the coated fluorescent layer can be uniform.
However, in the coating process using the rotary method, since the fluorescent material applying and drying processes are performed in a state where only three to five glass tubes are mounted on the disk-shaped stage, it is difficult to mass-produce the fluorescent lamps. Furthermore, since a worker loads the glass tubes on the stage one by one, and when the coating process is finished, separates the glass tubes from the stage one by one, the working process is complicated and the holding time excessively increases.
Particularly, when the fluorescent solution applied on the inner surface of the glass tubes is dried, the hot air is supplied only into the glass tube. Therefore, there is a temperature difference between the outer and inner surfaces the glass tube.
Furthermore, there is also a temperature difference between the hot air inlet and outlet. As a result, a thickness of the fluorescent layer is not uniform and a surface of the fluorescent layer is uneven.